How to check ruby version inside docker container - ruby-on-rails

Question

I have build the docker container by creating below docker file
# Select ubuntu as the base image
FROM ubuntu
# Install nginx, nodejs and curl
RUN apt-get update -q
RUN apt-get install -qy nginx
RUN apt-get install -qy curl
RUN apt-get install -qy nodejs
RUN echo "daemon off;" >> /etc/nginx/nginx.conf
# Install rvm, ruby, bundler
RUN curl -sSL https://get.rvm.io | bash -s stable
RUN /bin/bash -l -c "rvm requirements"
RUN /bin/bash -l -c "rvm install 2.1.0"
RUN /bin/bash -l -c "gem install bundler --no-ri --no-rdoc"
# Add configuration files in repository to filesystem
ADD config/container/nginx-sites.conf /etc/nginx/sites-enabled/default
ADD config/container/start-server.sh /usr/bin/start-server
RUN chmod +x /usr/bin/start-server
# Add rails project to project directory
ADD ./ /rails
# set WORKDIR
WORKDIR /rails
# bundle install
RUN /bin/bash -l -c "bundle install"
# Publish port 80
EXPOSE 80
# Startup commands
ENTRYPOINT /usr/bin/start-server
When i go inside the container and give the command ruby -v it throws bash: ruby: command not found
Could any one help me in doing this

Answer 1

I've spent a bit of time messing with RVM, Ruby and Docker recently. This answer might not be what you're looking for, but it needs to be said anyway: if you don't absolutely need RVM, then don't use it in your docker file. You've already noticed one downside: having to pre-empt your commands with /bin/bash -lc. You'll run into another downside if you ever want to have a non-root user run a ruby program in your Docker container. Also, your problem is most likely related to Docker not loading .bashrc or .bash_profile (I forgot which one RVM modifies) when you run a bash shell.
Instead use this to compile Ruby from source:
RUN apt-get update
RUN apt-get install -yq build-essential openssl libreadline6 libreadline6-dev curl git-core \
zlib1g zlib1g-dev libssl-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt-dev \
autoconf libc6-dev ncurses-dev automake libtool bison subversion libmysqlclient-dev
ADD http://cache.ruby-lang.org/pub/ruby/2.1/ruby-2.1.2.tar.gz /tmp/
RUN cd /tmp && tar -xzf /tmp/ruby-2.1.2.tar.gz
RUN cd /tmp/ruby-2.1.2/ && ./configure --disable-install-doc && make && make install
RUN rm -rf /tmp/*
ADD http://production.cf.rubygems.org/rubygems/rubygems-2.4.1.tgz /tmp/
RUN cd /tmp && tar -xzf /tmp/rubygems-2.4.1.tgz
RUN cd /tmp/rubygems-2.4.1 && ruby setup.rb
RUN rm -rf /tmp/*
RUN echo "gem: --no-ri --no-rdoc" > ~/.gemrc
RUN gem install bundler --no-rdoc --no-ri

Answer 2

You are not setting the default ruby after installing RVM. Trying setting the default ruby after installing it.
RUN /bin/bash -l -c "rvm install 2.1.0"
RUN /bin/bash -l -c "rvm use 2.1.0 --default"